Common tolerance codes for capacitors: J = ± 5%; K = ± 10%; M = ± 20%.
Common value code for capacitors: Two numbers, and a third number c, where c tells you the number of zeroes behind the first and second number. Usually, the result is to be read in pF.
Sometimes, there's also a value expressed in pF or µF, and you have to guess which is right. Some examples:
A ceramic capacitor with the number "470" on it likely has 470 pF, because ceramic caps are still mostly used for small-ish values.
"0.47" doesn't make sense in pF, because 0.47 pF would be too small for almost any practical use, so pretty much all capacitors labeled "0.47" will have a value of 0.47 µF = 470 nF.
"470" on a large-ish film or electrolytic capacitor will likely mean the cap's value is 470 µF.
(And even more strange markings do exist...)
Now, let's use your capacitors' markings as examples for this - here's what I guess:
103M Z5U 2-3KV ARC GAP KAP CHINA
10 * 103 pF = 10 000 pF = 10 nF. M: ± 20%
Z5U is the type of dielectric. This is a pretty creepy type of ceramic with huge tolerances over voltage and temperature.
NPO 7.5D IKV
7.5 is a fairly uncommon value for a capacitor. Mostly, you find values from the E6 or E12 series, hardly anything else. However, 7.5 is part of the E24 series, so it is not entirely alien, and according to this source, D would mean you have a tolerance of ± 0.5 pF. NP0 is a very good type of ceramic mostly used for values below 10...100 pF (that 0 in NP0 is a zero; I remember to have read that NP0 means negative-positive-zero, i.e. nearly zero tolerance over temperature and voltage changes). I guess your cap has 7.5 pF. That I is likely a 1, meaning the maximum voltage for this cap is 1 kV.
CM 1000M 125L
Maybe 1000 pF = 1 nF, with a tolerance of ± 20 % (M).
27 * 101 pF = 270 pF. Maximum Voltage: 2 kV.
Z5U 4700M IKV
Another one with a cheap type of ceramic (Z5U), probably 4 700 pF = 4.7 nF. Tolerance: ± 20 % (M). Max. Voltage: 1 kV.
Again, this is guess-work. Unfortunately, there is no standard that all manufacturers adhere to, so to be exactly sure, you would have to measure your devices and find the original data sheets with the device marking specifications, which can be very, very annoying.
Even more examples from similar questions: Identifying Capacitors, https://electronics.stackexchange.com/questions/10474/what-kind-of-capacitor-is-this